Method for electroslag remelting with slag introduction and equalized plural electrode remelting

ABSTRACT

In an electroslag remelting installation, a pair of consumable electrodes are immersed into a molten slag bath contained in a mold, which can be cooled by various arrangements of cooling liquid. The molten slag is introduced into the mold through a passage through the lower portion of the mold. AC electrical power is applied between the electrodes to cause current flow through the electrodes and through the molten slag bath and part of the molten metal pool, thereby heating and causing the electrodes to melt to form an ingot. As the electrodes melt, they are simultaneously fed together into the slag bath. A conductor, connected between the bottom plate of the mold and either a center tap on the secondary winding of the transformer supplying AC power to the electrodes or to a center tap on a choke coil connected in parallel with the secondary winding, provides an equalizing circuit which automatically adjusts the melting of the electrodes to keep them at equal immersion depths in the slag bath. Electrical lines and connectors are grouped in close arrangement and in parallel paths where possible to avoid inductance losses.

United States Patent" v119.1 1111 3,838,200

Paton et al. 1*Sept. 24, 1974 METHOD FOR ELECTROSLAG REMELTING WITH SLAG INTRODUCTION [30] Foreign Application Priority Data AND EQUALIZED PLURAL ELECTRODE Dec. 24, 1966 U.S.S.R 1118607 REMELTING Dec. 24, I966 -U.S.S.R 1118608 [75] Inventors: Boris Evgenievich Paton; Vladimir 1 Konstantinovich Lebedev; Boris U-S. Cl. Izraileyich Medovar; Jury Cl- Vadimovich Latash; Oleg petmvic [5 8] Field of Search 13/9 ES Bondarenko; Vitaly Mikhailovich Baglai; Mikhail Nikolaevich [56] References Cited Sidorenko, all of Kiev; Semen UNITED STATES PATENTS Abramovich Leibenlon; Gary 3,389,208 6 1968 Roberts et al 13/9 ES Petmvich Kaganovsky, both of 3,709,283 1i1973 Paton et al. 13/9 ES Zaporozhie; Andrei Pavlovich Altgauzen Moscow; Leonid 7 Primary Examiner-Roy N. Envall, Jr.

Evgenievich Nikolsky MOSPOW; Attorney, Agent, or Firm-Strauch, Nolan, Neale, Nies Zoya Alexandrovna Gorymna, & Kurz Moscow; Ljudmila Andreevna Safronova, Moscow; Leonid Savvich [57] ABSTRACT Katsevich, Moscow; Lev Avramovich volokhonsky Moscow; In an electroslag remeltmg 1nstallat1on, a pan of con- Alexandr Alexandrovich Nikulin, g sumable electrodes are immersed into a molten slag Moscow; wadimir Dmitrievich bath contained in a mold, which can be cooled by var- Artemiev, MOSCOW; Vladimir ious arrangements of cooling liquid. The molten slag is Mikhailovich Edemsk'y, introduced into the mold through a passage through Moskovskaya; Georgy the lower portion of the mold. AC electrical power is Alexandmvich VomninMoscow n applied between the electrodes to cause current flow of through the electrodes and through the molten slag bath and part of the molten metal pool, thereby heatl Asslgneei lnsmut Elekvtmsvarkl -E-O- ing and causing the electrodes to melt to form an in- Patona, Klev, got. As the electrodes melt, they are simultaneously Notice; h portion of the term of this fed together into the slag bath. A conductor, conpatem subsequent to Jan 9 1990 nected between the bottom plate of the mold and eihas been disclaimed ther a center tap on the secondary winding of the transformer supplying AC power to the electrodes or [22] Flledi 1972 to a center tap on a choke coil connected in parallel [21] Appl 298,949 I with the secondary winding, provides an equalizing circuit which automatically adjusts the melting of the Related 5- Appllcatlon D electrodes to keep them at equal immersion depths in [60] Division of Ser. No. 87,044, Nov.- 5,, 1970, the slag bath. Electrical lines and connectors are abandoned, which is a continuation-in-part of Ser. grouped in close arrangement and in parallel paths 1 1 P 23, 1970, 3,709,283, where possible to avoid inductance losses. which is a continuation of Ser. No. 676,873, Oct. 20, I I967, abandoned. 19 Claims, 7 Drawing Figures mam 2 sum luv '4 FIG.

SIIEUBN 4 PAIENTEB 85 241914 m wE N 0 PAIENTEDSEPZMW mam-'00 I smuur METHOD FOR ELECTROSLAG REMELTING WITH SLAG INTRODUCTION AND EQUALIZED PLURAL ELECTRODE REMELTING CROSS-REFERENCE TO RELATED APPLICATIONS This application is a division of application Ser. No. 87,044 (now abandoned), filed Nov. 5, 1970, which is in turn a continuation-in-part of copending application Ser. No. 76,205, filed Sept. 28, 1970, (now U.S. Pat. No. 3,709,283) which is a continuation of application Ser. No. 676,873, (now abandoned) filed Oct. 20, 1967 for Method of Electroslag Remelting of Metals and Alloys.

BACKGROUND OF THE INVENTION The present invention relates to the electroslag remelting of metals and alloys in a cooled mold from two consumable electrodes or two groups of such electrodes.

In particular, disclosed in Belgian Pat. No. 670,299 is a similar installation, capable of producing ingots of a fairly highquality.'I-Iowever', that disclosed installation does not include several features of the present invention and primarily fails to teach the criticalfeature by which equality of electrode melting is attained.

The known installation, disclosed in the abovementioned Belgian patent, is provided with a mold placed on a bottom plate, in which a slag bath is prepared by any conventional method. Two consumable electrodes or two groups of consumable electrodes are immersed into this'bath, that is, one pair or groups of pairs of consumable electrodes, said electrodes being connected in series to the secondary winding of a single-phase power transformer, employed as a power supply source for the installation, the electrodes being moved together during the operation by a feeding mechanism while being melted in the slag bath. The aforenoted Belgian patent describes but does not show a primer plate which is placed on a source plate or the bottom plate of a mold when a single electrode is being remelted in order to prevent the bottom plate from burning out under the start-up arcing condition. Such a primer plate is also known as a sacrificial plate and is not connected or secured in an electrically sound fashion to the bottom plate because it is intended to function only as an ablationshield for single electrode operation to protect the mold bottom plate.

The specified remelting conditions are maintained by controlling the magnitude of current and voltage by transferring the electrodes and switching over thevoltage stages of the transformer, respectively.

In some cases, however, in the process of electroslag remelting, as carried out in the existing installations, the equality of linear speeds of melting of each electrode or'electrodes' of each two groupsmay be disturbed. These disturbances may be caused, for exam ple, by a local difference in the cross-sections of the electrodes by the presence of porosity therein, and a misalignment of electrodes with respect to the mold.

In case of a long-time disturbance of the.equality in the linear speeds of melting the electrodes, a gradually increasing misalignment of the electrodes is observed such that one of the electrodes may happen to be immersed into the liquid metal-bath, i.e., an emergency mode of operation of the installation is possible. When unequal melting of the electrodes results in one electrode being longer (immersed deeper than the other one) the smooth functioning of a production melting run is interrupted. Then a special technique must be employed with attendant heavy investment of operator time and with the danger of an incomplete melting run.

To eliminate said disadvantages, it was required to provide an installation for the electroslag remelting of consumable electrodes, in which the electrodes would be connected in the electric circuit of the power transformer in such a manner that their melting during the operation be uniform.

SUMMARY OF THE INVENTION The present invention features an installation for the electroslag remelting of two consumable electrodes or two groups of consumable electrodes, which are connected in series into the circuit of. the power supply source, and are immersed into a slag bath prepared in a mold being placed on a cooled bottom plate. When pairs of plural consumable electrodes are remelted ac cording to the present invention, the upper ends of the electrodes of one group of plural electrodes are connected to one terminal of the power supply source and theupper ends of the other group of plural electrodes are connected to the other terminal of the power supply source so that for every effective pair of electrodes, one of the electrodes is connected to one terminal of the power supply source and the other electrode of the pair is connected to the other terminal of the power supply'source. In this manner a single power supply source provides operating current for plural pairs (or a pair of groups) of electrodes. These electrodes are moved together by a common feeding mechanism while being melted in the slag'bath. In conformity with the invention, a conductor of equalizing current is made to connect the supply source to the slag bath being prepared in the mold.

It is advisable to connect one end of the conductor of equalizing current to the point of half-voltage of the secondary winding of the transformer of said power supplyso'urce, while the other end thereof is connected to the bottom plate or the mold.

If for some reasons it is impossible to tap off the point of half-voltage of the secondary winding of the transformer, one end of the conductor of equalizing current may be connected to the point of half-voltage, of the winding of a choke, which is connected in parallel with the secondary winding of the transformer. The other end of the conductor of equalizing current is also connected either to the bottom plate or the mold.

When remelting in the installation, designed according to the present invention, entirely identical electrodes, disposed strictly symmetrically relative to the mold; the current of the same magnitude isflowing through each-of the electrodes; the same amount of power is evolved at each electrode immersedin the liquid slag; the depth of immersion of the electrodes into the slag bathis the same, and the conductor of equalizing current is deenergized. In the equalized state the.

conductor for equalizing current functions as a potential corrective element in the remelting system, and during the equalized mode of operation currentflows from the power source through one or more of the electrodes of the. pairs of electrodes into the molten slag bath and thence into the other electrode of each of the pairs of electrodes.

In case of misalignment of the electrodes due to a short-time influence of any of the above said factors, the intensity of current, flowing in the electrode immersed deeper into the slag bath, becomes higher than that of current flowing through the electrode immersed to a smaller extent, the difference being equal to the magnitude of equalizing current, which will then flow through the conductor of equalizing current. The ihtensity of the current flowing in the electrodes varies primarily according to changes in the resistance paths offered through each of the electrode sub-circuits. Generally, the electrode which extends furthest into the molten slag bath will provide the path of least resistance for the operating current and hence will have a larger current flow, than the current flow through the other electrode which will result in a relative cooling of that other electrode.

On account of such a variation in the'currents flowing through the electrodes, the power evolved at the electrode immersed deeper into the slag bath will be greater than that at the electrode immersed to a smaller extent. This will result in eliminating the misalignment and reducing the equalizing current to zero.

In the case of permanently acting factors, causing the misalignment of the electrodes, such a ratio of currents is established in the electrodes, with which the electrodes melt down at equal linear speeds, with equal or close values of immersion of the electrodes into the liquid slag.

The installation of the invention makes it possible to effect the electroslag remelting of two consumable electrodes or two groups of consumable electrodes, fed simultaneously into one mold without any misalignment of the electrodes under the action of any of the above-mentioned causes which bring about the in equality in the linear speeds of melting of the electrodes, and also to completely eliminate the possibility of an emergency operation.

Another feature of the present invention, includes the utilization of the equalization circuit with the aspect of introducing molten slag into the bottom of the remelting zone in the furnace mold, as defined by the lower portion of themold and its associated bottom plate, in an amount sufficient for the molten slag to achieve a predetermined depth in said remelting zone.

Because the slag is bottom poured into the remelting zone, the electrodes can already be in place and can be energized so that current beginsto flow and melting of the electrodes begins as soon as the slag reaches its predetermined depth at which it has risen to contact and complete a circuit between the lower ends of the electrodes. Voltage can be applied to the electrodes previously or simultaneously with the pouring of the slag. When a sufficient amount of slag has been introduced into the remelting zone so that the uppermost surface of the slag contacts the lowermost end of the electrodes, an electric circuit is completed between the electrodes and between the electrodes and the bottom plate, and the process of remelting the consumable electrodes begins. When the circuit is thus completed, and current commences to flow, that current flow is a signal that the slag has reached its predetermined depth and molten slag pouring is discontinued. Once remelting begins, it is continued until the electrode has been entirely melted and an ingot of refined metal is produced.

The bottom pouring of molten slag is an operation which is sufficiently fast, and current flow begins sufficiently quickly after the pouring commences, that the formation of a slag crust on the bottom of the remelting zone is prevented, accordingly false starts are eliminated. In fact, the time required for obtaining molten slag in the remelting zone with energized electrodes in place is minimized.

Because the electrodes can be positioned in the mold before pouring commences, and because pouring past the electrodes is not required, the gap between the electrodes and the remelting zone walls can be made very small. This factor permits that large crosssectional area electrodes can be used and the height of the tower required is accordingly reduced. In addition, the circuit lines can be shorter and thereby, the inductance of the circuit is reduced and the power factor of the system is accordingly increased. Since the slag is poured into the bottom of the remelting zone, the possibility of formation of slag scale on the remelting zone walls is entirely eliminated.

With this technique of pouring the molten slag into the bottom of the remelting zone, the'operator controlling the pouring can determine very precisely when to stop pouring the molten slag because current flow in the electrode circuit indicates to the operator that the slag bath has reached the predetermined depth, because the slag can be poured quickly through a closed channel into the bottom of the remelting zone, there is little opportunity for the slag to react with nitrogen in the air or to dissolve moisture from the air. Because slag is poured into the bottom of the remelting zone, a pouring ladle can be positioned near the base of the zone thus greatly reducing danger to personnel.

.T he initial predetermined distance between the consumable electrodes and the bottomplate is essentially the same as the predetermined initial depth which the slag achieves in the remelting zone. These are not exactly the same because slight additional molten slag will enter the remelting zone between the time when the circuit completion is signalled and the time when the discontinuance of the slag pouring is actually implemented. Accordingly, the bottom of the electrodes is positioned just below the desired slag level as the molten slag is poured.

According to this feature of the invention the molten slag is poured into the remelting zone through a bottom-pouring device which comprises a pouring funnel and a conduit attached to and in communication with a passage into the mold at the bottom portion thereof. A convenient passage can be formedin the bottom plate but a passage through the mold sidewall is also us able for enabling the bottom pouring technique to be practiced. 7

According to another feature of this invention, the bottom plate of the mold can be provided with a recess into which a piece of metal designated a weld lug of the same composition as the ingot is fitted. When remelting begins in the molten slag bath, the weld lug projects up into thebottom portionof the mold and its upper end will melt and weld to the ingot; Excellent electrical contact will thus be obtained between the base plate and the ingot, aiding the production of a sound ingot.

The bottom-pouring device can be used with or without the inclusion of the weld lug.

It is, therefore. an object of the present invention to provide a method of bifilar electroslag remelting with equalization of current between the power source for each of the pair or pairs of electrodes and the mold whereby the electrodes can be caused to melt at the same melting rate in order to maintain an equivalent linear dimension at all points during the melting operation and to provide for a convenient start-up procedure wherein molten slag is bottom-poured into the remelting zone of the mold with the consumable electrodes disposed in place within the mold by pouring the molten slag through a bottom pouring device connected to the mold.

Yet another object of the present invention is to provide for good electrical contact between the ingot being formed by the remelting of the consumable electrodes and the bottom plate of the mold by providing a weld lug which is in good electrical contact with the bottom plate and disposed with a portion thereof in the remelting zone located at the bottom portion of the mold.

Further novel features and other objects of this invention will become apparent from the following'detailed description, discussion and the appended claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS Possible embodiments of the invention will now be described by way of example with reference to the accompanying drawings, where in:

FIG. 1 represents an installation for the electroslag remelting according to the invention, wherein the bottom plate is connected by means of a conductor of equalizing current to the point of half-voltage of the secondary winding of a single-phase power transformer;

FIG. 2 represents the same installation, wherein the bottom plate is connected by means of a conductor of equalizing current to the point of half-voltage of the winding of an equalizing choke connected in parallel to the secondary winding of the single-phase transformer;

sition relative to the bottom pouring inlet port;

FIG. 6 is a schematic view of an ESR installation with an equalizing connection to a center tap of a transformer secondary winding similar to that illustrated in FIG. 1 and showing details of how the power supply lines are fed to the tower and thence to the electrodefurnace circuit; and I FIG. 7 is a schematic view similar to FIG. 6 but showingdetails of power line installation where a choke is used. I

SPECIFIC DESCRIPTION Y In the embodiments of the invention, represented in FIGS. 1 and 2, theinstallation is provided with a supporting column 1 mounting a mechanism 2 for feeding electrodes 3 and 4, to be introduced together intoa slag bath 5, as prepared in a mold 6 intended for shaping an ingot 7, built up from electrodes 3 and 4.

The mold 6 is placed on a bottom plate 8 and connected with a liftingmechanism 9 mounted on the column l.

The electrodes 3 and 4 are connected in series to a single-phase power transformer 10, or 10 in FIGS. 1 and 2, respectively, being the supply source of the installation, said electrodes being moved simultaneously by the mechanism 2 while melting down in the slag bath 5. One end of a conductor 11 of equalizing current is connected to the bottom plate 8, while the other end.

thereof is connected to the point C of half-voltage of the secondary winding 12 of the single-phase power transformer 10, as shown in FIG. 1.

In case the conductor 11 of equalizing current cannot, for some reasons, be connected to the point C of half-voltage of the secondary winding of the singlephase power transformer 10, an equalizing choke 13 can be employed, to be connected in parallel with said secondary winding 12 of the transformer 10'. The conductor ll of equalizing current is'then connected to the point C of half-voltage of a winding 14 of the equalizing choke 13, as it is shown in FIG. 2, and to the mold bottom plate 8. g

The equalizing choke 13 operates as an autotransformer having the transformation ratio equal to two.

The principle of operation of the installation of the invention is described in conformity with the installation, as illustrated in FIG. 1, whose equivalent electrical circuit diagram is represented in FIG. 3. On the diagram of FIG. 3, numerals 15 and 16 correspondingly designate the resistances of slag in the circuit, constituted by the electrode 3 slag metal bath and mold slag electrode 4, while the resistance of slag between the electrodes is indicated by numeral 17.

As it is obvious from the diagram, current flows in the slag bath 5 through two circuits via the resistance 17 and the resistances l5 and 16.

When the electrodes are immersed into the liquid slag at an equal depth, the resistances l5 and 16 are of equal value, the equalizing current in the conductor 11 is absent, since the drop of voltage across the resistance 15 and resistance 16 (the resistances of the short circuit to each electrode andthe resistances of the electrodes being not shown in the equivalent diagram) are equal to each other and to the halfvoltage of the secondary winding 12 of the transformer, i.e., the points.

A and C are points of the same potential.

In this case the installation operates according to a purely bifilar circuit diagram, the same current flowing through each electrode. 7 e

In case of a short-time action of one or a plurality of factors causing the inequality in the linear speeds of melting of the electrodes, one of the electrodes is immersed into the slag to a greater depth than the second one. For example, the electrode 4 will be immersed to a greater depth. Then the value of resistance 16 will be decreasedas compared with the resistance 15, because the distance e between the end of theelectrode 4 and metal bath 18 will be smaller than the distance e between this bath and the end of electrode 3. Owing to the fact that the resistance 16 is smaller than the resistance 15, a portion of the current of the'electrode 4 will flow, by-passing the electrode 3, in the conductor ll to the point of half-voltage of the secondary winding 12 of the transformer 10. Thus a greater amount of power will be evolved in the slag at the electrode 4 than that at the electrode 3, which will result in an increase in the speed of melting of the electrode 4 and in a decrease in the speed of melting of the electrode 3, i.e., in the elimination of the misalignment.

FIG. 4 shows an electroslag remelting apparatus with additional details and in which a tower 22 has two electrodes 23 and 24 retained in an electrode holder 26, powered by lifting mechanism 27, from which they depend into a mold 28 which, in turn, rests on a modified bottom plate 30. The lower vertically shifting carriage 32 can be used to lift the body of mold 28 upward and away from its bottom plate 30 after remelting of electrodes 23 and 24 into an ingot in the moldin a manner similar to that described for the furnace shown in FIG. 1. During the remelting process, the lower carriage 32 and its rigid support arms 34 provide stationary support for mold 28.

The modified bottom plate 30 has a centrally disposed recess 36 in which a cuboid or short cylindrical weld lug 38 is disposed. The weld lug 38 is forced into good electrical surface contact with the side wall surface or surfaces of recess 36 by a clamping rod 40 which extends through a lateral passage 42 provided in bottom plate 30 from the recess 36 to an outside edge location on the periphery of the bottom plate. An adjustment means 44, illustrated as a hand wheel, is provided at the exterior end of clamping rod 40 for adjusting the clamping force applied to weld lug 38. Suitable threaded fittings 46 are provided for the clamp rod 40. Material from which the weld lug is made has the same composition as the ingot to be formed by melting of electrodes 23 and 24 under the slag bath. The preferred disposition of the electrodes 23 and 24 will be 90 from the disposition shown in FIG. 4, the FIG. 4 disposition being shown in a way to better illustrate the two electrodes.

Mold 28 as with many ESR molds is made with an annular coolant channel 50 which is supplied with a coolant fluid (usually water) through ports 52 and 54 located at the bottom and top of mold 28, respectively. Bottom plate 30 is fitted with a coolant subassembly 56 which consists of a substantially coextensive underplate 58 and side members 60 and 62, shown schematically in cross-section as outside walls of conduits which are releasably connected to bottom plate 30 and underplate 58. The coolant subassembly 56, abutted up against the bottom of bottom plate 30 forms coolant channel 64. The molds in the assemblies of FIGS. 1, 2, 6 and 7, for convenience are not illustrated with coolant passages, nevertheless, they are made with coolant means similar to those described for FIG. 4. g

A bottom pouring device 70 is shown connected to base plate 30 and is constructed as an upstanding funnel 72 connected to an upwardly disposed conduit 74 which is, inturn. connected by its base flange 76 thereof to bottom plate 30. Conduit 74 forms a passage 78 which is connected to a passage 80 formed in bottom plate 30. Passage 80 terminates in aperture 82 located within mold 28 adjacent to the mold wall and directed into the remelting zone defined by the inner surfaces of the mold side walls and its bottom plate in the bottom portion of the mold. The conduit 74, as shown, can be preferrably made tapered with the large end down in order to facilitate removal of the bottom pouring device from the remaining elements of FIG. 4 and to enable clean-out after a remelting run.

Molten slag poured into the receiving hopperor funnel 72 of the bottom pouring device 70 immediately flows down the vertically disposed pouring device conduit 74, within its defined passage 78 and through the horizontal channel or passage in the bottom plate which exits through access port 82 into the electroslag furnace remelting zone. At start-up the remelting zone is located in the bottom portion of the furnace mold as defined by its side walls and bottom plate. The bottom pouring device provides a smooth start-up for the furnace installation.

The modifications shown and described relative to FIG. 4 can be employed in any of the furnace mold structures shown in FIGS. 1, 2, 3, 6 and 7, as desired. The weld lug 38vcan be used in conjunction with bottom pouring device 70 or can be used alone. Similarly, the bottom pouring device 70 can be used with or without the weld lug 38 and its associated elements.

The weld lug 38 provides for continuous good electrical contact between the ingot 7 (FIG. 1), which will be formed on the base plate 8 or 30, and the equalizing conductor 11. Equalizing current conductor 11 is connected between the center tap position of the secondary winding 12 of power transformer 10 to the bottom plate 8 preferrably ata point opposite the mounting of the bottom pouring device 70.

FIG. 5 shows an arrangement of two rectangular cross-section electrodes in a square mold to form a square ingot as discussed in Belgian Pat. No. 670,299. The bottom pouring device 70 can be in line with the vertical axial plane between the electrodes, as shown, or can be perpendicular thereto.

As also disclosed in Belgian Pat. No. 670,299, the electrodes employed in the electroslag remelting startup system described herein can be either of square, rectangular, circular or semi-circular cross-section. The preferred embodiment is to use one pair of electrodes each of square cross-section or one pair of electrodes each of rectangular section to produce an ingot of rectangular or square cross-section and furthermore,

it is possible to use two pairs of square or rectangular cross-section electrodes as shown in FIG. 6 of the identified Belgian Patent.

The weld lug 38 and the bottom pouring device 70 can be provided in the more detailed manner as shown and described in US. application Ser. No. 68,661, filed Sept. 1, 1970 for Method for Electroslag Remelting of Metals With Slag Introduction, FIGS. 3, 4, 5, 6 and 7.

When constant factors are acting, causing the misalignment an equalizing current will constantly flow through the conductor of equalizing current, said current being sufficient for equalizing the linear speeds of melting of theelectrodes, the values of the depths of immersion of the electrodes being close.

The installation for the-electroslag remelting, according to the present invention, allows the elimination of the misalignment of the electrodes irrespective of factors causing it; the installation also permits remelting of electrodesmade of metals featuring different melting points, completely eliminating the possibility of an emergency operation. g

The installation of the invention permitted a stable process at equal linear speeds of melting of electrodes with a small misalignment of the electrodes, provided the differences between the cross-sectional areas of the electrodes is equal to 20 percent. The magnitude of the equalizing current amounted to 18 percent of the'intensity of current flowing through the electrode of a smaller cross-sectional area.

Yet theremelting of electrodes, having such a difference between the cross-sectional areas, proves to be impracticable in the conventional installation, provided with the mechanism for simultaneous feeding of the electrodes, because in the course of the melt the depth of immersion of the electrode with a greater crosssectional area gradually increases, and the electrode end is thus immersed into the metal bath.

FIGS. 6 and 7 correspond to the installation depicted, respectively, in FIGS. 1 and 2 and illustrate how the electric power cables feed from the transformer units to the electrodes and mold assembly in a manner which keeps inductance losses to a minimum. Reference numerals identifying similar components are used.

in FIGS. 1 and 6 and also in FIGS. 2 and 7.

The flexible electric power cables 100 and 102 have end lugs 104 and 106, respectively, which are bolted to end plates on respective bus bars 108 and 110 of the secondary winding terminals of the transformer 10. The other ends of cable 100 and 102 also have respective end lugs 112 and 114 which'are connected via bolts to terminal plates of power connections 116 and 118 mounted on the upper lifting carriage or dolly 2, and individual bus bars from the power connections 116 and 118 provide connections to the dual electrode clamping head 120 and thence to the individual electrodes 3 and 4. Details of insulated bifilar electrode connections can be seen in the aforedescribed Belgian Pat. No; 670,299.

In FIG. 6, bus bar 126 is connected to the center tap C of the transformer secondary winding and an equalizing current conductor cable 111 has one lug end 130 connected as by bolts to the bus bar 126. The other lug end 132 of equalizing current conductor cable 111 connects via a terminal block connector 134 mounted at a location adjacent the power connection 116 and 118 on the upper lifting carriage 2. From terminal block connector 134 the aforedescribed equalizing current conductor 11, a flexible cable, extends down to a connection 140 on the mold bottom plate 8.

All three electric supply cables 100, 102 and 111 are led from the transformer terminals in a hanging bundle held with suitable clips 142. The bundle loop'of the cables permits arelatively short electrical path while permitting raising and lowering of the upper lifting dolly mechanism 2 and keeping inductance losses to a minimum.

TheFIG. 7' installation is structurally quite similar to that described for FIG. 6 excepting that the transformer secondary winding has no center tap connection so only the'two secondary power cables 100 and 102' lead to the power connections 116' and 118. In this installation, the equalizing circuit is provided by the center tapped choke 13 mounted by suitable supports 148 on the upper dolly mechanism 2..By suitable bus bar connections 150 and 152, the choke is parallel connected to the power connections 1 16' and 118' and a bus bar connection 154 from the choke center tap C" 'connects to the equalizing terminal block connector 134 mounted on the upper dolly mechanism 2, and from the terminal block collector 134", the aforedescribed equalizing current conductor 11 extends to a connection 140 on the mold bottom plate 8'. With the choke so mounted on the dolly 2'. inductance losses are reduced even more from those present in the installation of FIG. 6 because the necessary electrical lead for the equalizing circuit is much shorter. In ESR systems, the power cables are often water cooled electrical lines which have lug ends enabling connection by having two connection lugs at either end portion or it can be made in the form of a direct fixed position bus bar having openings in the ends for connecting bolts. If desired it can also be a water cooled cable.

OPERATION Operation is described with reference to a basic installation such as illustrated .in FIG.'1. Consumable electrodes 3 and 4 are placed in the electrode holder of feed mechanism 2 which is attached to the upper portion of the tower or column 1 and are raised to a position where their lower ends are above the top of a mold to be put in place. The mold 6 is moved into position under the electrodes and in engagement with and is secured tothe extending arms of lower lifting mechanism 9 of column 1. Upper feed mechanism 2 is then operated to lower the electrodes until their lower ends are a predetermined distance above the mold bottom plate 8. In a run for which a weld lug 38 (FIG. 4) is to be employed, such a weld lug will be previously placed in its recess 36 in the bottom plate and forced into contact with the sidewall of the recess by means of the clamping rod and adjustment means 44.

Power transformer 10 is energized, a slag pouring container (not shown), which contains molten slag, is

I brought up to mold 6 and the molten slag poured into the bottom pour funnel 72 (see FIG. 4) until the molten slag bath within the mold raises to a height where it contacts the lower end of electrodes 3 and 4. Such contactmakes a circuit connection between electrodes and completes the working power circuit to permit flow of electric current from electrode to electrode through the slag bath. The current flowthrough the resistance of the slag bath heats the slag bath, and the tips or ends of the electrodes, and allows them to be remelted to form a metal pool and subsequently the metal ingot 7 around weld lug 20 on the bottom plate 8. When a bottom pouring device 70 is not employed, the slag must be top poured into mold 6 prior to energizing the transformer.

During the melting operation, the electrode feed mechanism 2 is used to lower both consumable electrodes 3 and 4 into the mold in a controlled manner so that the tips will always 'be in contact with and partially submerged within the slag bath 5. The rate at which the electrodes descend into the molds is controlled through operation of feed mechanism 2. Electric current travels from the terminals of the secondary winding of 'transformer l0 betweenthe consumable electrodes through the slag bath 5 and partially across the metallic bath 18. After obtaining an ingot of the required height, the operation is terminated. To achieve this termination, de-

scending movement of the electrodes is interrupted and transformer power is turned off, whereupon the feed mechanism 2 with the electrode head is raised to the upper position and the electrode stubs are removed from the mechanism. After the upper molten pool of metal at the top end of the ingot has hardened, the mold 6 may then be raised by the lower lifting mechanism 9 to remove it completely from the ingot. The bottom plate 8 carrying the ingot is then moved away from the melting position, as by the wheeled dolly arrangement illustrated, and the ingot removed therefrom. Passages 78'and 80 of the bottom pouring device'70and in the base plate 30 are cleaned of hardened slag and after replacing the weld lug 38 the same base plate may be moved back into position and the mold 6 lowered onto the plate for the next remelting run.

The electroslag remelting apparatus herein before described and disclosed assures that all parts of the circuit, namely, the current conducting terminals, the flexible cables necessary to carry the current to the electrodes and the consumable electrodes themselves are in close parallel arrangement. The close, parallel arrangement of the current carrying paths guarantees good electrical compensation of the circuit formed by the current carrying elements and results in a considerable reduction in the induction losses which are experienced in conventional single electrode remelting equipment wherein the conducting elements form a single circuit loop. By greatly reducing the induction losses, the power factor is significantly raised to above 090. In addition, since the working current is not directed through the base plate of the mold, it is not necessary to use metallic primer plates or sacrificial plates. Hence, the remelting process is rendered more economical. Another material advantage in the present arrangement is that the possibility of shunting the current across the wall of the mold toward the upper surface of the molten bath is excluded whereby fissures and stringers are eliminated.

With regard to using plural pairs of consumable electrodes, it is possible to arrange two pairs of square cross-sectional electrodes in an equally spaced manner in a square cross-section ingot. In such a mode of operation each end of the secondary winding of the power supply transformer is directly connected to a pair of electrodes by auxiliary conductors from common terminal points. In the manner above described, the two pairs of electrodes can be mounted onto a single electrode holder to move the simultaneously. The base plate employed can be modified for bottom pouring in the manner illustrated in FIG. 4. Also, the base plate can be modified to include a weld lug as shown in FIG.

'4. These two modifications can be used for operation either with a single pair of electrodes or with plural pairs of electrodes. In either case, a conductor from the center tap of the secondary winding of the power transformer to the base plate and in turn to the weld lug means, when it is used as shown in FIG. 4, is included in the apparatus to maintain self-corrective equality of melting rates among the electrodes. For a discussion of bifilar electroslag remelting apparatus without the equalization circuit see Belgian Pat. No. 670,299.

In addition to the above mentioned mechanical elements and electrical systems, the electroslag remelting system can include a gas exhaust system by which gases emitted during the remelting can be removed from the vicinity of the top of the mold; an operating console supplied with fittings, indicators and controls in order to permit an operator to control the various operational components of the system and the electrical supply means from a common location.

In previously known installations in which there is mechanism for simultaneous feeding of the electrodes, operation of the installation, where there is a difference between the electrode cross-sectional areas, proves to be impractical because in the course of the melt, the depth of immersion of the electrode with the greater cross-sectional area gradually increases, and that electrode end becomes immersed into the metal bath.

The invention may be embodied in other specific forms without departing from the scope, spirit, or essential characteristics thereof. Present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope and spirit of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are, therefore, intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

l. A method of electroslag melting of metals and alloys in a molding unit comprising: introducing slag in molten state into the molding unit through a passage through the lower .portion of the molding unit in an amount sufficient for the slag to achieve a predetermined depth in the start-up melting zone; depending consumable electrode means including at least one pair of consumable electrodes into the molding unit so that there will be contact between the electrodes and the molten slag; connecting at least one consumable electrode of the consumable electrode means to a first terminal of a secondary current circuit of a single-phase transformer; connecting the other consumable electrode of the consumable electrode means to a second terminal of the secondary current circuit: connecting an equalizing current circuit to the molding unit from a voltage source from the transformer having a value between that of the first and second terminal connection points of the secondary current circuit of the transformer: passing current between the electrodes and through the molten slag bath, whereby current flow is provided through the equalizing current circuit to maintain equality of melting rates of each of the electrodes of the electrode means.

2. A method as defined in claim 1, wherein the slag is introduced into the start-up melting zone in the molding unit from the lowermost boundary of the startup zone.

3. A method as defined in claim 1, wherein the slag is introduced into the melting zone in the molding unit at a point below the location of the lowermost end of the electrodes when depending into the molding unit.

4. A method as defined in claim 3, wherein the elec trodes are depending into the molding unit and are energized during introduction of the slag.

5. A method as defined in claim 1, wherein said molding unit includes a bottom plate, the electrodes are connected to an AC power circuit with the current equalizing circuit connected to the .bottom plate whereby the current flowing through the electrodesis automatically increased and decreased by the equalizing circuit to maintain equal rates of melting for the electrodes.

6. A method as defined in claim 5, wherein the current equalizing circuit is a circuit made from a center tap connection on a secondary winding of the single phase transformer.

7. A method as defined in claim 1, wherein current flow through the equalizing circuit increases total melt ing rate of the electrodes as well as maintaining equality of melting rates between the electrodes.

8. A method as defined in claim 1, wherein the con sumable electrode means including at least the pair of consumable electrodes is moved as a unit into the mol ten slag bath for melting.

9. A method of electroslag melting of metals and alloys in a molding unit comprising: introducing slag in molten state into a cooled molding unit with a bottom plate through a passage through the lower portion of the molding unit in an amount sufficient for the slag to achieve a predetermined depth in the start-up melting zone; depending consumable electrode means, *two or two groups thereof forming a pair, into the molding unit so that there will be contact between the electrodes and the molten slag; connecting at least one consumable electrode of the consumable electrode means to a first terminal of a power supply source; connecting the other consumable electrode of the consumable electrode means to a second terminal of the power supply source in order to connect the power supply source in series with the pair of electrodes and the molten slag bath: providing current flow between each electrode or group of electrodes and the other electrode or group of electrodes of the pair, the current flow between the electrodes consisting of single phase current flow: providing an equalizing current circuit from the power supply source to the molten slag bath from a voltage source having a value between that of the first and second terminal connection points: passing current between the pair of electrodes and through the molten slag bath, whereby current flow is provided through the equalizing current circuit to maintain equality of melting rates of each of the electrodes of the electrode means. 7

10. A method as defined in claim 9, wherein the consumable electrode means including at least the pair of consumable electrodes is moved as a unit into the molten slag bath for melting.

11. A method for electroslag melting of metals and alloys in mold means having a bottom at the lower end thereof. comprising in the initiation of the melting process, the steps of; disposing at least a pair of consumable electrode means within the mold means with the lower electrode ends in a melting zone of themold means and spaced apart from the bottom; heating slag outside the mold means; introducing the slag in molten state into the mold means through passage means at the lower part of the mold means and in an amount sufficient for the molten slag to achieve a depth within the mold means; causing the molten slag and the lower electrode ends to come into contact with one another, and with the electrodes in contact with the molten slag providing a series current flow from a power supply means between at least the pair of electrodes and through the molten slag, said current flow between said electrodes consisting of single phase AC current flow;

providing an equalizing current circuit connected between the mold means and the power supply means, the current flowing through the electrodes being increased and decreased by the equalizing circuit to maintain equal rates of melting for the electrodes.

12. A method of electroslag melting as defined in claim 11, wherein the consumable electrode means are initially positioned with their lower ends at a predetermined distance above the bottom boundary of the melting zone.

13. A method of electroslag melting as defined in claim 12, wherein the consumable electrode means are positioned with their lower ends a predetermined dis tance from the bottom boundary of the melting zone less than the depth which the molten slag achieves in the melting zone.

14. A method of electroslag melting as defined in claim 11, wherein the molten slag is introduced into the melting zone at a point below the lowermost ends of the electrode means.

15. A method of electroslag remelting as defined in claim '14, wherein the electrode means are energized during introduction of the molten slag.

' 16. A method of electroslag remelting as defined in claim 11, comprising the additional steps of pressing a weld lug against a side wall of a recess in the inner wall of the bottom of the mold means within the remelting zone to provide electrical contact between the weld lug and the mold means.

17. A method of electroslag remelting as defined in claim 16, including providing the equalizing current flow through a circuit directly connected to the weld lug.

18. A method of electroslag remelting as defined in claim 16, including making the weld lug of the same the bottom of the'mold means. 

1. A method of electroslag melting of metals and alloys in a molding unit comprising: introducing slag in molten state into the molding unit through a passage through the lower portion of the molding unit in an amount sufficient for the slag to achieve a predetermined depth in the start-up melting zone; depending consumable electrode means including at least one pair of consumable electrodes into the molding unit so that there will be contact between the electrodes and the molten slag; connecting at least one consumable electrode of the consumable electrode means to a first terminal of a secondary current circuit of a singlephase transformer; connecting the other consumable electrode of the consumable electrode means to a second terminal of the secondary current circuit: connecting an equalizing current circuit to the molding unit from a voltage source from the transformer having a value between that of the first and second terminal connection points of the secondary current circuit of the transformer: passing current between the electrodes and through the molten slag bath, whereby current flow is provided through the equalizing current circuit to maintain equality of melting rates of each of the electrodes of the electrode means.
 2. A method as defined in claim 1, wherein the slag is introduced into the start-up melting zone in the molding unit from the lowermost boundary of the start-up zone.
 3. A method as defined in claim 1, wherein the slag is introduced into the melting zone in the molding unit at a point below the location of the lowermost end of the electrodes when depending into the molding unit.
 4. A method as defined in claim 3, wherein the electrodes are depending into the molding unit and are energized during introduction of the slag.
 5. A method as defined in claim 1, wherein said molding unit includes a bottom plate, the electrodes are connected to an AC power circuit with the current equalizing circuit connected to the bottom plate whereby the current flowing through the electrodes is automatically increased and decreased by the equalizing circuit to maintain equal rates of melting for the electrodes.
 6. A method as defined in claim 5, wherein the current equalizing circuit is a circuit made from a center tap connection on a secondary winding of the single phase transformer.
 7. A method as defined in claim 1, wherein current flow through the equalizing circuit increases total melting rate of the electrodes as well as maintaining equality of melting rates between the electrodes.
 8. A method as defined in claim 1, wherein the consumable electrode means including at least the pair of consumable electrodes is moved as a unit into the molten slag bath for melting.
 9. A method of electroslag melting of metals and alloys in a molding unit comprising: introducing slag in molten state into a cooled molding unit with a bottom plate through a passage through the lower portion of the molding unit in an amount sufficient for the slag to achieve a predetermined depth in the start-up melting zone; depending consumable electrode means, two or two groups thereof forming a pair, into the molding unit so that there will be contact between the electrodes and the molten slag; connecting at least one consumable electrode of the consumable electrode means to a first terminal of a power supply source; connecting the other consumable electrode of the consumable electrode means to a second terminal of the power supply source in order to connect the power supply source in series with the pair of electrodes and the molten slag bath: providing current flow between each electrode or group of electrodes and the other electrode or group of electrodes of the pair, the current flow between the electrodes consisting of single phase current flow: providing an equalizing current circuit from the power supply source to the molten slag bath from a voltage source having a value between that of the first and second terminal connection points: passing current between the pair of electrodes and through the molten slag bath, whereby current flow is provided through the equalizing current circuit to maintain equality of melting rates of each of the electrodes of the electrode means.
 10. A method as defined in claim 9, wherein the consumable electrode means including at least the pair of consumable electrodes is moved as a unit into the molten slag bath for melting.
 11. A method for electroslag melting of metals and alloys in mold means having a bottom at the lower end thereof, comprising in the initiation of the melting process, the steps of: disposing at least a pair of consumable electrode means within the mold means with the lower electrode ends in a melting zone of the mold means and spaced apart from the bottom; heating slag outside the mold means; introducing the slag in molten state into the mold means through passage means at the lower part of the mold means and in an amount sufficient for the molten slag to achieve a depth within the mold means; causing the molten slag and the lower electrode ends to come into contact with one another, and with the electrodes in contact with the molten slag providing a series current flow from a power supply means between at least the pair of electrodes and through the molten slag, said current flow between said electrodes consisting of single phase AC current flow; providing an equalizing current circuit connected between the mold means and the power supply means, the current flowing through the electrodes being increased and decreased by the equalizing circuit to maintain equal rates of melting for the electrodes.
 12. A method of electroslag melting as defined in claim 11, wherein the consumable electrode means are initially positioned with their lower ends at a predetermined distance above the bottom boundary of the melting zone.
 13. A method of electroslag melting as defined in claim 12, wherein the consumable electrode means are positioned with their lower ends a predetermined distance from the bottom boundary of the melting zone less than the depth which the molten slag achieves in the melting zone.
 14. A method of electroslag melting as defined in claim 11, wherein the molten slag is introduced into the melting zone at a point below the lowermost ends of the electrode means.
 15. A method of electroslag remelting as defined in claim 14, wherein the electrode means are energized during introduction of the molten slag.
 16. A method of electroslag remelting as defined in claim 11, comprising the additional steps of pressing a weld lug against A side wall of a recess in the inner wall of the bottom of the mold means within the remelting zone to provide electrical contact between the weld lug and the mold means.
 17. A method of electroslag remelting as defined in claim 16, including providing the equalizing current flow through a circuit directly connected to the weld lug.
 18. A method of electroslag remelting as defined in claim 16, including making the weld lug of the same composition as the ingot which is formed in said mold means.
 19. A method as defined in claim 11, including providing a path for the equalizing current flow through the bottom of the mold means. 